From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from eggs.gnu.org ([2001:4830:134:3::10]:60805) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1bwvFx-0006e9-8z for qemu-devel@nongnu.org; Wed, 19 Oct 2016 14:06:26 -0400 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1bwvFt-0002Oi-CU for qemu-devel@nongnu.org; Wed, 19 Oct 2016 14:06:25 -0400 Received: from mx1.redhat.com ([209.132.183.28]:36282) by eggs.gnu.org with esmtps (TLS1.0:DHE_RSA_AES_256_CBC_SHA1:32) (Exim 4.71) (envelope-from ) id 1bwvFt-0002OM-4q for qemu-devel@nongnu.org; Wed, 19 Oct 2016 14:06:21 -0400 Received: from int-mx10.intmail.prod.int.phx2.redhat.com (int-mx10.intmail.prod.int.phx2.redhat.com [10.5.11.23]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mx1.redhat.com (Postfix) with ESMTPS id 447DF5455D for ; Wed, 19 Oct 2016 18:06:20 +0000 (UTC) Date: Wed, 19 Oct 2016 19:06:16 +0100 From: "Dr. David Alan Gilbert" Message-ID: <20161019180616.GF2035@work-vm> References: <20161018135213.GI2190@work-vm> <20161018140141.GF12728@redhat.com> <87wph4g44n.fsf@dusky.pond.sub.org> <20161019081210.GA2035@work-vm> <20161019084235.GE11194@redhat.com> <87twc8d60e.fsf@dusky.pond.sub.org> <20161019100552.GD2035@work-vm> <20161019101616.GL11194@redhat.com> <87a8e0bkl6.fsf@dusky.pond.sub.org> <20161019122158.GS11194@redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20161019122158.GS11194@redhat.com> Subject: Re: [Qemu-devel] chardev's and fd's in monitors List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , To: "Daniel P. Berrange" Cc: Markus Armbruster , qemu-devel@nongnu.org * Daniel P. Berrange (berrange@redhat.com) wrote: > On Wed, Oct 19, 2016 at 02:16:05PM +0200, Markus Armbruster wrote: > > "Daniel P. Berrange" writes: > > > > > On Wed, Oct 19, 2016 at 11:05:53AM +0100, Dr. David Alan Gilbert wrote: > > >> > > >> We need a way to be able to report an error without plumbing error_setg > > >> up the stack; if you're saying error_report isn't suitable then we > > >> should just recommend we switch everything in migration back to > > >> fprintf(stderr, > > > > In the cases where error_report() isn't suitable, fprintf() is just as > > unsuitable for the exact same reasons. > > > > > Well both error_report() + fprintf are broken from POV of anything > > > using QMP. error_report() is slightly less broken for HMP, > > > > error_report() is not broken at all for HMP code. The trouble is code > > that can't know whether it's running in a context where error_report() > > is suitable. > > > > > but doesn't > > > help QMP. > > > > Correct. > > > > > In the short term we should just make error_report be threadsafe in > > > its usage of the monitor. > > > > Any problems left once cur_mon is thread-local (which it should be > > anyway)? > > If we make cur_mon a thread-local, then error_report() is equivalent > to fprintf(stderr) for the migration code, since the migration > code runs in a different thread thread, and so would always see > cur_mon == NULL. Yes, that would become safe; it does sound the best fix for the current worry. If we had that, then why not wire up error_report to pass errors back to QMP as well? Dave > > > Beyond the short term we have no choice but > > > to plumb in error_setg throughout, otherwise QMP will continue to > > > have useless error reporting in this area of code. > > > > Actually, no choice but propagate errors up the stack until they reach a > > spot that knows how to report them. error_setg() is *one* way to do > > that. Its prime advantage is ability to carry an error message. Its > > disadvantage is boilerplate. Use it as needed. Just don't convert back > > and forth between Error and other representations while propagating up > > the stack. > > Regards, > Daniel > -- > |: http://berrange.com -o- http://www.flickr.com/photos/dberrange/ :| > |: http://libvirt.org -o- http://virt-manager.org :| > |: http://entangle-photo.org -o- http://search.cpan.org/~danberr/ :| -- Dr. David Alan Gilbert / dgilbert@redhat.com / Manchester, UK